It has taken me 5 more months than Peter to wonder, as he did in November 2004, why it is one never hears about someone having cancer of the heart. Cecil’s answer was that the heart appears to be protected from cancer by the rapid and continuing rate of cell regeneration. So now, does anyone have the answer as to how we might use this knowledge to encourage rapid rate of cell regeneration in all other parts of the body? Could that mechanism be used to “flush out” cancer when it occurs, e.g. in the liver, pancreas, brain? Alternatively, could “heart cells” be replicated and transfused into the body to confuse the cancers, or would they just hang around for a while and then die? ElizabethJ.
According tothis site heart cancer does occur.
In sort of a reverse answer, I just watched a documentary about how adult stem cells are being used to treat, among other things, cardiac damage. Often, after a heart attack, some of the heart tissue is damaged and no longer pumps correctly. The show I saw showed how doctors could inject bone marrow, with its blood stem cells, directly into the heart, and the stem cells would cause new tissue to grow to replace the damaged heart tissue. Quite interesting, really. If it pans out, it will be a quick, easy, cheap, safe way to heal, well, broken hearts.
Cancer, in the form of sarcoma, does occasionally occur in the heart. I have personally seen one case of it.
For whatever reason, sarcomas (malignant tumors of the soft tissues, such as muscle [including the heart], blood vessels, cartilage, fatty tissue) are rarer than carcinomas (malignant tumors of epithelium, which generally includes what most people think of as “cancer”, i.e. breast cancer, lung cancer, colon cancer, prostate cancer, etc.).
I’m not sure I buy the “rapid and continuous regeneration” protective hypothesis, for two reasons:
-
Mucosal surfaces (such as the colonic lining) are constantly regenerating as old lining cells are sloughed off, and yet cancer (carcinoma) occurs in them at a much higher frequency than in the soft tissues, which do not undergo such rapid cell division and turnover. This makes sense to me; the more often you have to replicate your DNA, the higher the chances that a mutation will occur.
-
Heart muscle cells actually have fairly limited regenerative properties, which is why scarring after a heart attack is such a big problem. When a part of the heart muscle dies in a heart attack, the remaining muscle cells don’t regenerate and fill in that area; a scar forms instead. This scar does not have the functionality of regular heart muscle (doesn’t contract, and can be structurally weaker).
So I would actually submit that it’s the heart’s lack of continuous cell replication that is the protective factor against development of tumors.
The dogma is that cardiac myocytes are completely post-mitotic, and that, unlike skeletal muscle, no pool of resident stem cells exists to regenerate it. That dogma may have to be revised a little bit, but for greatly the most part, adult cardiac myocytes don’t divide, and require rather dramatic genetic abnormality to overcome the built-in checks that keep them exited from the cell cycle. It’s very difficult for cells that do not divide to accumulate the chromosomal damage necessary to become transformed. There probably are stem cells, both resident in the myocardium, and perhaps recruited from other places like bone marrow, that are responsible for a very low level of regenerative maintainance of heart muscle (though they are completely inadequate to repair even minor damage). The primary means of coping with damage in the heart is through hypertrophy, which is simply the enlargement of existing cardiac myocytes, and scarring.
Maligancies of cardiac myocyte lineage are virtually unheard of except in people with a congenital disorder, and usually manifest as part of a more generalized syndrome like Carney’s complex. I believe the term for these sorts of tumors is a myxoma, and except for rare atrial myxomas, they’re usually benign (though still dangerous, because of where they might be). Most other tumors seen in the heart are angiosarcomas that are derived from endothelial cells also found in or around the heart.
Cardiac myxomas are indeed the most common type of primary cardiac tumor, and they are benign (although, as you note, they may cause problems due to location). As I noted above, I have seen one case (an autopsy) of a primary sarcoma of the heart (in a patient without, as far as I know, any congenital syndrome), which was noteworthy in that the malignant cells were producing osteoid (technically, this might have qualified it as a primary cardiac osteosarcoma). I don’t have my list of references on cardiac sarcomas handy, although it’s probably still paperclipped to that report.
There are also the very rare pulmonary artery trunk sarcomas, which I don’t remember much about save the name.
Link to column: http://www.straightdope.com/classics/a941125.html
Might be worth appending it to the OP.